# Derived Tag Against OPC Structures

**URL:** <https://forum.inductiveautomation.com/t/derived-tag-against-opc-structures/75622>\
**Category:** Ignition Early Access\
**Tags:** ignition81\
**Created:** [June 28, 2023, 7:39am UTC](https://forum.inductiveautomation.com/t/derived-tag-against-opc-structures/75622 "2023-06-28T07:39:55Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![deon.korb](https://avatars.discourse-cdn.com/v4/letter/d/8c91f0/32.png) [@deon.korb](https://forum.inductiveautomation.com/u/deon.korb)\
**Post date:** [June 28, 2023, 7:39am UTC](https://forum.inductiveautomation.com/t/derived-tag-against-opc-structures/75622/1 "2023-06-28T07:39:55Z")

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Continuing the discussion from [Nightly 8.1 Changelogs - 2023](https://forum.inductiveautomation.com/t/nightly-8-1-changelogs-2023/68524/86):

> [@Nightly 8.1 Changelogs - 2023](https://forum.inductiveautomation.com/t/nightly-8-1-changelogs-2023/68524/86):
>
> ### Tags & UDTs
> 
> **IGN-6843: Derived Tags Against OPC Structures causing high CPU and Memory use**  
> Improved memory and CPU usage of Document Tags.

We use this extensively (~500k tags on a gateway) by reading struct as document tags from Siemens OPC UA servers. Obviously we didn't know it causes high memory and CPU as this is what it is.

Are there any side effects we should specifically look out for and test against prior to upgrading to 8.1.30 eventually?

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**Author:** ![paul-griffith](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/paul-griffith/32/37249_2.png) [@paul-griffith](https://forum.inductiveautomation.com/u/paul-griffith)\
**Post date:** [June 28, 2023, 4:18pm UTC](https://forum.inductiveautomation.com/t/derived-tag-against-opc-structures/75622/2 "2023-06-28T16:18:42Z")

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The gist is that, as much as possible, mutable 'views' of the original source document(s) are made, instead of deeply copying them every time they're adjusted only slightly.

So it should be pretty clear to you if something isn't working, because you'll start getting unexpected values or outright errors. It might be a good idea to check the nightly build, though our QA team did some very thorough testing.